The presently disclosed embodiments relate in general to electrostatography comprising improved features in the imaging member that enhance functional properties when used in the electrostatographic imaging system. These embodiments pertain to, more particularly, an electrophotographic imaging member which has improved imaging layer(s) formulated to comprise a charge transport compound and a novel polymer blended binder. The novel polymer blended binder used in the imaging layer(s) is a binary polymer blend as described herein to give two distinctive binder blended formulations and properties.
The three polymer blended binder formulations are: (1) a binary polymer blended binder formed to consist of blending a film forming bisphenol polycarbonate and a film forming organic acid terminated A-B diblok copolymer to impart imaging member photoelectrical tune-ability result, (2) a binary polymer blended binder formed to consist of a blend of the film forming bisphenol polycarbonate and the organic acid terminated A-B diblock copolymer plus a slippery nano size silicon oxide particle dispersion to render the resulting imaging member surface lubricity for contact friction reduction and photoelectrical tune-ability/wear resistance enhancement, and (3) a binary polymer blended binder formed to consist of blending the film forming organic acid terminated A-B diblock copolymer and a polysiloxane containing low surface energy copolymer to impart imaging member photoelectrical stability as well as surface adhesiveness/slipperiness/contact friction reduction. In the present disclosure, slipperiness refers to a property of cleaning apparatus or machine contacting subsystems that allows such apparatus or subsystems contacting the imaging member to easily slide over the surface. Adhesiveness is the opposite of adhesion, namely, that material contact on the surface does not stick to the surface but is rather easily removed.
The novel polymer blended binders formulated according to the description in the embodiments of present disclosure provide the resulting imaging member with specific benefits of photo-electrical tune-ability, copy printout quality improvement, chemical amine contaminant protection, as well as surface energy lowering result for contact friction reduction. The imaging layer(s), for example the charge transport layer(s), formulated as described herein are applicable for all types of electrophotographic imaging members used in electrophotography to provide effective imaging member service life extension in the field.
In electrophotographic reproducing apparatuses, including digital, image on image, and contact electrostatic printing apparatuses, a light image of an original to be copied is typically recorded in the form of an electrostatic latent image upon a photosensitive member and the latent image is subsequently rendered visible by the application of electroscopic thermoplastic resin particles and pigment particles, or toner. Typical electrophotographic imaging members include, for example: photoreceptors commonly utilized in electrophotographic (xerographic) imaging process systems. All of the electrophotographic imaging members are prepared in either flexible belt form or rigid drum configuration. For typical flexible electrophotographic imaging member belt, it comprises a charge transport layer, a charge generating layer, and optional layers on one side of a flexible supporting substrate layer and does also include application of an anticurl back coating on the opposite side of the substrate to render imaging member flatness and complete the imaging member structure. Alternatively, the electrophotographic imaging members can also be prepared as rigid member, such as those utilizing a rigid substrate support drum. For these drum imaging members, having a thick rigid cylindrical supporting substrate bearing the imaging layer(s), there is no exhibition of the curl-up problem, and thus, there is no need for an anticurl back coating layer.
The flexible electrophotographic imaging members may be seamless or seamed belts. Seamed belts are usually formed by cutting a rectangular sheet from a web, overlapping opposite ends, and welding the overlapped ends together to form a welded seam.
Although the scope of the present embodiments covers the preparation of both types of electrophotographic imaging members, in either flexible belt design or rigid drum configuration, for reasons of simplicity, the discussion hereinafter will focus only on flexible electrophotographic imaging member belts.
One type of flexible composite photoconductive layer used in xerography is illustrated in U.S. Pat. No. 4,265,990 which describes a photosensitive imaging member having at least two electrically operative layers. One layer comprises a photoconductive layer which is capable of photogenerating holes and injecting the photogenerated holes into a contiguous charge transport layer. Generally, the two electrically operative layers are supported on a conductive layer support substrate, with the photoconductive layer being sandwiched between a contiguous charge transport layer and the supporting conductive layer. In this negatively charged imaging member, the charge transport layer is the top outermost exposed layer. In the alternative imaging member design, the charge transport layer is, however, sandwiched between the supporting electrode and a photoconductive layer. Since the typical flexible electrophotographic imaging members exhibit undesirable upward imaging member curling-up after completion of the electrically operative layers, the application of an anticurl back coating onto the backside of the support substrate is necessary to provide the appropriate imaging members with desirable flatness.
The flexible photosensitive members having at least two electrically operative layers, as disclosed above, provide excellent electrostatic latent images when charged in the dark with a uniform negative electrostatic charge, exposed to a light image and thereafter developed with finely divided electroscopic marking particles. The resulting toner image is usually transferred to a suitable receiving member such as paper or to an intermediate transfer member which thereafter transfers the image to a receiving member such as paper.
In the case where the charge generating layer is sandwiched between the top outermost exposed charge transport layer and the electrically conducting layer, the outer surface of the charge transport layer is charged negatively and the conductive layer is charged positively. The charge generating layer then should be capable of generating electron hole pair when exposed image wise and inject only the holes through the charge transport layer. In the alternate case when the charge transport layer is sandwiched between the charge generating layer and the conductive layer, the outer surface of the charge generating layer is charged positively while conductive layer is charged negatively and the holes are injected through from the charge generating layer to the charge transport layer. The charge transport layer should be able to transport the holes with as little trapping of charge as possible. In flexible imaging member belt such as photoreceptor, the charge conductive layer may be a thin coating of metal on a flexible substrate support layer.
As more advanced, higher speed electrophotographic copiers, duplicators and printers were developed, however, degradation of image quality was encountered during extended cycling. The complex, highly sophisticated duplicating and printing systems operating at very high speeds have placed stringent requirements including narrow operating limits on photoreceptors. For example, the numerous layers used in many modern photoconductive imaging members should be highly flexible, adhere well to adjacent layers, and exhibit predictable electrical characteristics within narrow operating limits to provide excellent toner images over many thousands of cycles. Typically, negatively charged multilayered flexible photoreceptor that has been employed as a belt in electrophotographic imaging systems comprises a flexible substrate, a conductive layer, an optional blocking layer, an optional adhesive layer, a charge generating layer, a charge transport layer and a conductive ground strip layer adjacent to one edge of the imaging layers. In such a photoreceptor, it does usually further comprise an anticurl back coating layer on the backside of the substrate (opposite the side carrying the conductive layer, support layer, blocking layer, adhesive layer, charge generating layer, charge transport layer, and other layers) to effect curl control for rendering flatness configuration and give a complete structure.
Since the charge transport layer in a negatively charged imaging member is the top outermost exposed layer, it is constantly subjected to machine cleaning blade and cleaning mechanical friction interaction brush under a normal machine electrophotographic imaging and cleaning processes condition, the charge has been found to develop pre-mature wear/scratch failure. In addition, the outer Charge transport layer is also exposed to chemical vapor contaminants interaction during electrophotographic imaging process in the field to negatively impact function. For example, exposure to the vapor amine species (from ammonia) emitted from common cleaning agents have been seen to interact with the imaging member charge transport layer, causing material degradation to promote pre-mature onset of charge transport layer cracking and exacerbation of wear failure which severely cut short the functional life of the imaging member. In one particular instant, amine vapor impact on copy printout quality degradation has recently been seen when pre-printed papers (papers having pre-printed images which employed amine agents catalyzed UV cured ink) are used by customers for subsequent addition of xerographic images over the pre-printed paper blank spaces; that is the accumulation of amine residues deposition onto the imaging member charge transport layer surface, after repeatedly making contact with receiving papers during xerographic imaging process, is found to cause ghosting image defects print-out in the output copies. Since ghosting image defects in the output copies are unacceptable print quality failures, so it does require frequent costly imaging member replacement in the field.
Additionally, the conventional flexible imagine member designs have an inherent photo-electrical function limitation; which is exhibition of progressive electrical property degradation of monotonously cycle-up under a normal machine electrophotographic imaging process condition. The continuation of imaging member electrical cyclic up is seen to gradually reach a point of onset of copy print failure that cuts short the imaging member service life.
With the issues described above, there is an urgent need to resolve these issues and extend the service life of the imaging member in the field. In particular, there is a need for a formulation of a charge transport layer that is resistive to amine specific effect to resolve the current pre-printed paper ghosting image defects print out problem.
Conventional photoreceptors are disclosed in the following patents, a number of which describe the presence of light scattering particles in the undercoat layers: U.S. Pat. No. 5,660,961; U.S. Pat. No. 5,215,839; and U.S. Pat. No. 5,958,638. The term “photoreceptor” or “photoconductor” is generally used interchangeably with the terms “imaging member.” The term “electrostatographic” includes “electrophotographic” and “xerographic.” The terms “charge transport molecule” are generally used interchangeably with the terms “hole transport molecule.”
In U.S. Pat. No. 7,413,835, there is disclosed an electrophotographic imaging member having a thermoplastic charge transport layer, a polycarbonate polymer binder, a particulate dispersion, and a high boiler compatible liquid. The disclosed charge transport layer exhibits enhanced wear resistance, excellent photoelectrical properties, and good print quality.
In U.S. Pat. No. 7,592,111, issued on Sep. 22, 2009 to Yu, et al., there is disclosed an imaging member formulated with a crosslinkable liquid carbonate for charge transport layer and overcoat layer binder formulation. The imaging electrostatographic member exhibits improved service life.